Messages in this thread | | | Date | Wed, 24 Apr 2019 16:49:24 +0200 | From | Petr Mladek <> | Subject | Re: [RFC][PATCH 1/2] printk: lock console_sem before we unregister boot consoles |
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On Tue 2019-04-23 15:25:10, Sergey Senozhatsky wrote: > The following pattern is not completely safe: > > for_each_console(bcon) > if (bcon->flags & CON_BOOT) > unregister_console(bcon); > > Because, in theory, console drivers list and console drivers > can be modified concurrently from another CPU. Take console_sem > lock, which protects console drivers list and console drivers, > before we start iterating console drivers list. > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 17102fd4c136..b0e361ca1bea 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -2777,62 +2819,34 @@ void register_console(struct console *newcon) > pr_info("%sconsole [%s%d] enabled\n", > (newcon->flags & CON_BOOT) ? "boot" : "" , > newcon->name, newcon->index); > - if (bcon && > - ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) && > - !keep_bootcon) { > - /* We need to iterate through all boot consoles, to make > + > + if (keep_bootcon) > + return; > + > + if (bcon && (newcon->flags & (CON_CONSDEV|CON_BOOT)) == CON_CONSDEV) { > + console_lock(); > + /* > + * We need to iterate through all boot consoles, to make > * sure we print everything out, before we unregister them. > */
I wondered if moving the console locking could break the above statement.
It seems that the comment has been invalid since the commit 8259cf4342029aad37660e ("printk: Ensure that "console enabled" messages are printed on the console").
Could we remove it in this patch? It touches it indirectly anyway.
Otherwise, the patch looks fine to me:
Reviewed-by: Petr Mladek <pmladek@suse.com>
> for_each_console(bcon) > if (bcon->flags & CON_BOOT) > - unregister_console(bcon); > + __unregister_console(bcon); > + console_unlock(); > + console_sysfs_notify(); > } > } > EXPORT_SYMBOL(register_console);
Best Regards, Petr
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